1. Field of the Invention
The present invention relates to a reset-out circuit, and more particularly, to a micro-controller with a reset-out circuit that allows feeding back the micro-controller reset-out signal to its reset-in input without locking the micro-controller into reset.
2. Discussion of the Prior Art
Micro-controllers typically have a reset state where various circuits of the micro-controllers are initialized prior to commencement of normal operation. For example, the reset state is entered when power is first applied or when certain internal or external conditions occur that cast doubt on continued proper operation of the micro-controllers. Entering the reset state initializes the micro-controller to a known state and allows proper operation thereafter.
A typical micro-controller has a reset-in input pin which receives an external reset signal to reset the micro-controller, e.g., due to a power interrupt. In addition to being reset by the external reset signal, the micro-controller is also reset due to internal conditions. The micro-controller outputs a reset-out signal from a reset-out output pin in response to either the external reset signal received at the reset-in input pin, or an internally generated reset signal. For example, the internal reset signal is generated by a central processing unit (CPU) of the micro-controller in response to execution of a reset instruction, by a timeout of a watchdog timer or by detection of certain error conditions.
It is desirable to use the micro-controller reset-out signal as a single global reset signal provided to all circuits of a device, since the micro-controller reset-out signal is generated in response to either the external or internal reset conditions. When used as a global reset, the micro-controller reset-out signal from the reset-out output pin is fed back to the reset-in input pin of the micro-controller, as well as to other devices in the system.
Feeding back the micro-controller reset-out signal to the micro-controller reset-in input pin presents the potential problem of locking the micro-controller into the reset state permanently. A further problem arises due to the short duration or pulse width of the global system reset signal provided from the micro-controller. A short global system reset signal may not properly reset all devices in a system.
Accordingly, there is a need for a circuit that allows proper operation of a micro-controller in response to both externally and internally generated reset signals where a global system reset output from the micro-controller reset-out output pin is fed back to the micro-controller reset-in input pin without locking the micro-controller in the reset state and causing other problems.